Safety venting mechanism for batteries

ABSTRACT

A battery comprises a battery cell having two voltage terminals and a flexible sidewall; a wall structure against which the battery cell is located, the wall structure including a sidewall that is adjacent to the sidewall of the battery cell; and a tooth structure that extends away from the sidewall of the wall structure and towards the sidewall of the battery cell, wherein the tooth structure includes a distal end sufficiently sharp to puncture the flexible sidewall of the battery cell when the flexible sidewall of the battery cell is forced up against the tooth structure due to a build up of excess pressure inside the battery cell.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application No. 61/143,976, filed Jan. 12, 2009 and entitled“Prismatic Battery Module With Scalable Architecture,” the entirecontents of which are incorporated herein by reference.

This application is also related to the following applications, filedconcurrently herewith, the entire contents of which are incorporatedherein by reference:

U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled“Methods of Welding Battery Terminals,”

U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled“Structure of Prismatic Battery Modules with Scalable Architecture,”

U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled“Prismatic Battery Module with Scalable Architecture,”

U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled“Bi-metallic Busbar Jumpers for Battery Systems,”

U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled“Fuse For Battery Cells,” and

U.S. patent application Ser. No. (TBA), filed on Dec. 1, 2009, entitled“Busbar Supports And Methods Of Their Use for Battery Systems,”

TECHNICAL FIELD

The present invention relates to battery modules and scalablearchitectures for manufacturing battery modules.

BACKGROUND OF THE INVENTION

A ‘battery module’ is a subassembly that is typically installed inside a‘battery pack’, which is an assembly that is installed in a terrain,marine, or aeronautic vehicle. These vehicles typically have a varietyof high power electric loads, such as a computer-controlled powerinverter driving an electric motor that is used for vehicle propulsionor some form of mechanical actuation.

A large group of battery modules can also be used by an electric utilitycompany to help equalize a local power distribution network's worst-casesupply fluctuation episodes. The modules are installed inside a ‘batterystation’, which is a large rigid stationary weather-proofclimate-controlled enclosure that is secured to a concrete foundation.The modules are mounted and electrically connected via racks with docksso that any module can be rapidly connected or disconnected.

Battery packs and battery stations typically have other subassembliesand components installed inside them in order to deliver completeend-item battery packs to vehicle manufacturers or complete end-itembattery stations to electric utility companies. These subassemblies andcomponents include electronic sensor modules, electronic controlmodules, electrical charging modules, electrical interface connectors,electrical fuses, electrical wiring harnesses, and thermal managementmeans.

BRIEF SUMMARY OF THE INVENTION

In general, in one aspect, a battery comprises a battery cell having twovoltage terminals and a flexible sidewall; a wall structure againstwhich the battery cell is located, the wall structure including asidewall that is adjacent to the sidewall of the battery cell; and atooth structure that extends away from the sidewall of the wallstructure and towards the sidewall of the battery cell, wherein thetooth structure includes a distal end sufficiently sharp to puncture theflexible sidewall of the battery cell when the flexible sidewall of thebattery cell is forced up against the tooth structure due to a build upof excess pressure inside the battery cell.

In embodiments of the battery, the battery cell is a prismatic batterycell.

In some embodiments, the distal end of the tooth is a point, and inothers, the distal end is an edge. In some embodiments where the toothis a point, the tooth further comprises a channel extending away fromthe region of the sharp feature to allow gases within the region of thepoint to move away from the battery cell. In other embodiments where thetooth is a point, the tooth further comprises a second sharp point and achannel between the first and second sharp points to allow gases betweenthe points to move away from the battery cell.

In certain embodiments, the first battery cell comprises a region ofincreased expandability relative to the rest of the battery cell, theregion defining a specific expansion path for the battery cell, andwherein the distal end is situated along the specific expansion path. Insome such embodiments, the region of increased expandability comprises aport exposing a puncturable portion of the battery cell, and in some ofthose embodiments, the tooth extends at least partially into the port.

Other embodiments include one or more of the following features. Whereinthe sidewall of the wall structure is a part of a heatsink. Wherein thesidewall of the wall structure is a busbar support that is mounted to aheatsink.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE FIGURES

For a fuller understanding of the nature and objects of the presentinvention, reference should be made to the following detaileddescription taken in connection with the accompanying drawings in whichthe same reference numerals are used to indicate the same or similarparts wherein:

FIG. 1 shows a battery module.

FIG. 2 shows a battery module with busbar covers and busbars removed andwith cell subassemblies exposed.

FIG. 3 shows a prismatic battery cell.

FIG. 4 shows a zipper fuse of a prismatic battery cell.

FIG. 5 shows a more detailed view of a cell subassembly.

FIG. 6 shows another view of a cell subassembly.

FIG. 7 shows an alternative heatsink and cell subassembly.

FIG. 8 shows another alternative heatsink and cell subassembly.

FIG. 9 shows a heatsink with attached pressure relief teeth.

FIG. 10 shows a view of a battery module pressure plate.

FIG. 11 shows a portion of a band component of a battery module.

FIG. 12 shows several busbar supports, attached to cell subassemblies ina battery module, including a reduced-height cell subassembly.

FIG. 13A shows a busbar support attached to a heatsink.

FIG. 13B shows an alternative busbar support to support one batterycell.

FIG. 14 shows several busbar supports attached to cell subassemblies ina battery module, each retaining at least a portion of a busbar jumper.

FIG. 15 shows a side profile of a busbar jumper.

FIG. 16 shows a busbar terminal in relation to pressure plate and cellsubassemblies.

FIG. 17 shows a busbar terminal attached to a pressure plate and abusbar bridge.

FIG. 18 shows a busbar terminal with two variations of clips forattachment of wiring.

FIG. 19 shows a side view of a wiring attachment clip.

FIG. 20 shows a support clip for attachment of a thermistor.

FIG. 21 shows a cutaway view of a busbar cover.

FIG. 22 shows a family of battery modules incorporating a scalablearchitecture.

FIG. 23 shows pressure relief teeth.

FIG. 24 shows several arrangements of busbar components that may be usedto achieve various configurations of battery modules.

FIG. 25 shows views of a configuration of a welding laser with respectto a busbar component.

FIG. 26 shows before and after views of the attachment of a busbarcomponent to a battery cell terminal.

DETAILED DESCRIPTION OF THE INVENTION

A battery module consists of an assembly of cell subassemblies, eachcontaining prismatic battery cells, where the cells are electricallyconnected to the other cells in the module to form the battery module.The term ‘prismatic’ refers to the shape of the battery cell that isdescribed herein and it differentiates this module from other moduleswith cylindrical battery cells.

FIG. 1 shows a battery module 10 with a negative terminal 20 and apositive terminal 21. The battery module 10 contains one or more cellsubassemblies 30. As described in more detail below, the cellsubassemblies are a basic building block from which battery modules ofarbitrary scales may be constructed. The cell subassemblies containprismatic battery cells (not shown), each of which provides a portion ofthe battery's electrical power and storage capacity. The cellsubassemblies 30 are held together by pressure plates 50 and bands 51.Pressure plates 50 act as a mounting mechanism for the battery module,and contain one or more mounting passages 52 to allow the module toaccept hardware (not shown) to mount the battery module 10 within, forexample, a battery pack enclosure or on a battery station's rack invarious mounting orientations. The individual battery cells areelectrically connected in parallel and/or series by busbars (describedbelow) which connect the cells to one another and to the terminals ofthe battery, all of which are on one side of the battery module. Thatside of battery module 10 is covered with one or more busbar covers 40.

FIG. 2 shows a battery module 10 with busbars and busbar covers removedto reveal a view of the inside of cell subassemblies 30. Eachsubassembly contains one or two prismatic battery cells 300, each cellhaving a positive terminal 301 and negative terminal 302. Terminals 301and 302 are connected electrically in series and/or parallel by busbarjumpers (not shown). Busbar terminals (also not shown) connect some ofthe battery terminals to either the battery module's negative terminal20 or positive terminal 21.

The prismatic battery module described herein has a group of identicalcells. The quantity of cells per module and the module's electricalconnection configuration (parallel count versus series count) definesthe module's electrical characteristics and performance ratings. Forexample, a module with a ‘23S3P’ configuration has sixty-nine (69)cells, twenty-three (23) subgroups that are electrically connected inseries, and three (3) cells in each subgroup that are electricallyconnected in parallel. Depending on the configuration, battery modulesmay contain either an even or an odd number of battery cells.

Prismatic Battery Cell

FIG. 3 shows a prismatic battery cell 300. A prismatic cell has twolarge flat surfaces, top surface 306 and bottom surface 307 (notvisible), that are basically parallel to each other and which are usedfor mechanical retention and thermal management inside the module. Thecell's enclosure may be referred to as a ‘pouch’ because it is anon-rigid flexible sheet that is folded and bonded to create acost-effective environmentally-sealed housing. The pouch's material is athin aluminum foil with a polymer coating applied to both surfaces. Thepouch is folded at the bottom edge which provides a seal boundary 303.The polymer coated pouch is formed into a thermally-bonded flange at thetwo sides, which creates two more seal boundaries 304 and 305. Thisarrangement decreases the module's physical volume without a decrease innet performance. The side flange's size is selected so as to ensurelong-term robustness. The cell's side flanges are folded to create acompact width.

The cell's two flat electrical terminals, positive terminal 301 andnegative terminal 302, protrude from one of the pouch's edges and theterminals are environmentally-sealed using electrically-isolativepolymeric perimeter seals. The remaining portion of the pouch's terminaledge is thermally-bonded to create a fourth environmentally-sealedboundary, which completes the cell's perimeter seal. The terminals arepositioned symmetrically with respect to the center axis 315, andpreferably the terminals are in the center plane of the battery cell.Accordingly, battery cell 300 may be “flipped” 180 degrees around centeraxis 315 with the result that each terminal is in the same position thatthe opposite terminal held prior to “flipping” the cell (relative toviewing the cell along axis 315 facing the edge containing the cellterminals). This symmetry allows one to stack up a series of cellswithout regard to whether the negative terminal is on the left or rightside (as viewed along center axis 315), and in either orientation theresulting rows of terminals will each be aligned in a straight row, andthus may be easily interconnected to one another. Specifically, batterymodules can be built with different combinations of series and parallelconnections by (1) selectively orienting the battery cells so that theterminals on the same left/right side of adjacent battery cells haveeither the same or opposite polarities; and (2) electrically connectinggroups of these adjacent terminals using busbar components (describedbelow) with connections between terminals of opposite polarities formingseries configurations and connections between same-polarity terminalsforming parallel configurations. The negative terminal's material iscopper and the positive terminal's material is aluminum to complimentthe cell's chemistry and internal construction. The terminal length issmall compared to other commercially-available designs. The opportunityto use compact terminals is clarified in the subsection entitled ‘BusbarComponents’. For the purpose of explanation, ancillary negative andpositive symbols have been added to the cell of FIG. 3.

The battery cell's non-rigid flexible pouch will physically expand if aworst case electrical overload incident occurs. Pressure relief (alsoknown as out-gassing) during an electrical overload incident may beprovided through the use of a “tooth” mounted externally to the cell,either as alternative to or in combination with pressure relief ventfeature 309. The tooth will puncture the cell in a controllable mannerif the cell were to expand into contact with it. This tooth is describedfurther below.

FIG. 4 shows zipper fuse 308 integrated into an electrical terminal 302of battery cell 300. Zipper fuse 308 includes two rows, each row made upof a slot-shaped hole 310 at one end of the row and circular-shapedholes 311 between the slot-shaped hole 310 and the other end of the row.This fuse is referred to as a ‘zipper’ fuse because looks like a zipper.The zipper fuse is incorporated in the cell's negative terminal. Thegeometry, number and position of the zipper fuse slot holes 310 andcircular holes 311 are selected so that the fuse actuates within aspecified time period that prevents a cascading failure mode with theadjacent cells or potentially all of the cells in a module.Specifically, the fuse slot holes help to ensure a consistent pattern offuse activation by concentrating current “hot spots” near the regionaround the holes, to promote fuse activation to start in those areas.The use of circular holes in addition to the slots helps, among otherthings, to maintain the structural integrity of the terminal prior tofuse activation. The positioning of the two parallel rows of slot holesand circular holes creates a region 312 between the rows that ispartially thermally isolated from the remainder of the terminal, whichconcentrates the heat developed during fuse activation to help make theactivation more complete and consistent.

Battery Subassembly

FIG. 5 shows a group of cell subassemblies, including subassemblies 30 aand 30 b. Subassembly 30 a includes a heatsink 400 a having two large,flat surfaces, as well as a battery cell 300 a which also has two large,flat surfaces. Battery cell 300 a is adjacently mounted to heatsink 400a such that the second large, flat surface of battery cell 300 a abutsthe first large, flat surface of heatsink 400 a. Subassembly 30 a alsoincludes a compliant pad 401 a having two large, flat surfaces and asecond battery cell 310 a having two large, flat surfaces. Compliant pad401 a is adjacently mounted to battery cell 300 a such that the firstlarge, flat surface of battery cell 300 a abuts the second large, flatsurface of compliant pad 401 a. Compliant pad 401 a is also adjacentlymounted to battery cell 310 a such that the first large, flat surface ofcompliant pad 401 a abuts the second large, flat surface of a secondbattery cell 310 a. This arrangement forms a repeating “cassette”configuration of a battery cell, a heatsink, another battery cell, and acompliant pad, followed by another grouping of a battery cell, aheatsink, another battery cell, and a compliant pad, and so on.Compliant pad 401 a helps to distribute pressure between thesubassemblies when they are banded together between the pressure plates,as well as allowing expansion/contraction of cells during use.Similarly, subassembly 30 b is mounted adjacently to subassembly 30 a.Subassembly 30 b includes a heatsink 400 b having two large, flatsurfaces, as well as a battery cell 300 b which also has two large, flatsurfaces. Heatsink 400 b is adjacently mounted to battery cell 310 asuch that the first large, flat surface of battery cell 310 a abuts thesecond large, flat surface of heatsink 400 b. Battery cell 300 b isadjacently mounted to heatsink 400 b such that the second large, flatsurface of battery cell 300 b abuts the first large, flat surface ofheatsink 400 b. Subassembly 30 b also includes a compliant pad 401 bhaving two large, flat surfaces and a second battery cell 310 b havingtwo large, flat surfaces. Compliant pad 401 b is adjacently mounted tobattery cell 300 b such that the first large, flat surface of batterycell 300 b abuts the second large, flat surface of compliant pad 401 b.

As shown in both FIG. 5 and FIG. 2, all of the heatsinks are bonded tothe adjacent cells during the module's assembly process via a dispensedcure-after-assembly adhesive that is also used to bond the compliantpads to the adjacent cells. The group of cells, pads, and heatsinkscreates the main stack subassembly for every module, which fosters ascalable architecture. In other words, one can readily change the sizeof the module by simply adding or subtracting identical subassemblies.The subassemblies may or may not be pre-assembled as such and then laterassembled together as sub-units into the battery module's main stack.The assembly of the main stack may be accomplished as a one-step processwhere all of the battery cells, heatsinks and compliant pads areassembled together in one process. The concept of a ‘subassembly’ isused as a convenient label for a logical group of components whendescribing the overall structure of the battery module.

Also as shown in FIG. 5, each of the battery cells (e.g., 300 a, 310 a,300 b and 310 b) are mounted on respective heatsinks (e.g., 400 a and400 b) with their positive terminals oriented on the left or right asviewed end on at the terminals. For example, in FIG. 5, battery cells300 a, 310 a, and 300 b are each oriented with their negative terminalsto the right from the perspective of FIG. 5, while battery cell 310 b ismounted with its positive terminal to the right. Other orientations ofgroups of battery cells (e.g., flipping battery cell 310 b 180 degreesso that its positive and negative terminals exchange positions) allowdifferent combinations of series or parallel connections between theterminals depending on which groups of adjacent terminals areelectrically connected by the busbar jumpers and terminals describedbelow.

FIG. 6 shows a view of a cell subassembly 30 from which battery module10 is built. FIG. 6 shows a heatsink 400 joined to a battery cell 300,which in turn is joined to a compliant pad 401. FIG. 6 does not show theadjacent cell that would be joined to compliant pad 401 as describedabove and in FIG. 5. Referring still to FIG. 6, when subassembly 30 isstacked adjacent to another subassembly, the metallic heatsink 400contacts two cells 300 and 310. Each cell contacts the heatsink via oneof the cell's two flat surfaces to facilitate thermal management viaconduction or forced convection heat transfer. This results in requiringonly about half the number of heatsinks per module as compared to usinga heatsink for each cell. The benefit is a compact module which has animproved power output/physical volume ratio compared to othercommercially available modules some of which have larger and moreelaborate heatsinks.

The heatsink is made from an aluminum sheet that is stamped and formedusing standard tooling practices. The heatsink has anelectrically-isolative coating to ensure that a worst-case electricaloverload incident does not allow an electrical short circuit path to anyor all of the heatsinks The coating thickness is preferably chosen so asto not substantially impede heat transfer. Protective coatings andapplication processes may be selected to simultaneously provide theelectrical short circuit protection during an electrical overloadincident, permit effective heat transfer, and reduce cost.

Another function of the heatsink is to protect the cells from foreignobjects during a severe vehicle crash. As discussed previously, theheatsink's formed wings 403 nest with an adjacent heatsink's profile toprovide a satisfactory level of cell protection with respect tocomplexity, cost, and the module's physical volume. These wings areformed by folding three of the heatsink's edges at approximately a rightangle to the large flat surfaces of the heatsink.

Referring now to FIG. 5, an indentation (404 a, 404 b) is formed fromthe heatsink by using additional bends near the area of the wing thatmeets the large flat surfaces of the heatsink to receive a portion of anadjacent heatsink's wings. For example, indentation 404 b is formed toreceive a portion of wing 403 a. This makes the heatsinks with theirinternal components easier to stack on top of one another. The batterypack's enclosure may be the major protection barrier during a crash, sothe heatsinks are another barrier to further improve the batterymodule's safety capability.

A second type of heatsink with short formed wings that envelop only onebattery cell (as opposed to the “full-height” heatsinks that envelop twocells) is used if a module has an odd cell count, where the second typeof heatsink is located at one end of the stack of subassemblies. Inthese odd cell count configurations, no battery cell is attached to thebottom of the bottom-most heatsink, as is shown in FIG. 5.

FIG. 7 shows this second type of heatsink 420 that nests into anadjacent cell subassembly 421. Heatsink 420 is joined to battery cell320 in the same manner as the full-height heatsinks are attached toadjacent cells. FIG. 7 also shows the use of two compliant pads, 422 aand 422 b, which are used at both ends of a module's main stack in orderto distribute and equalize the clamp force imparted to the stack by thepressure plates. This second type of heatsink is also used if a modulehas an even cell count, but even cell count modules also use a thirdtype of heatsink.

A third type of heatsink with medium-height formed wings that enveloponly one battery cell may also be used if a module has an even cellcount, where the third type of heatsink is located at one end of thestack of subassemblies opposite the end with the second type ofheatsink. In these even-cell-count configurations, this third type ofheatsink is nested adjacent to a heatsink that would otherwise have anexposed battery cell. For example, referring to FIG. 8, this third typeof heatsink 430 rests beneath the lower-most heatsink 429 to helpprotect a single battery cell 321 located between heatsinks 429 and 430.Two compliant pads (not shown) are adjacently mounted to each other, andone side of one of the compliant pads is adjacently mounted to heatsink430 at the end of the module's main stack of subassemblies.

While these additional types of heatsinks cause additional components tobe released and produced in the manufacturing process, they fullyrespect the principle that a heatsink contact every cell via one of thecell's two large flat surfaces, and that every cell be protected fromforeign objects during a severe vehicle crash.

FIG. 9 shows a heatsink 400 with pressure release teeth 410 and 411mounted through holes in the heatsink. One tooth 410 is oriented so thatits sharp end points toward one of the heatsink's attached batterycells, and if a second cell is joined to the heatsink, the other tooth411 is pointed toward that cell. An additional pair of teeth may bepositioned elsewhere on the heatsink 400 or on the busbar supportconnected to the heatsink. The tooth's material is molded plastic and itis either heat-staked or ultrasonically-welded to a plain hole in thestamped aluminum heatsink. If an electrical overload incident occurs,the cell's non-rigid flexible pouch will physically expand due to rapidinternal gas generation. As it expands, the force of the internalpressure will press the pouch against the tooth, puncturing the cell andproviding a controlled relief of the internal pressure. The battery cellhas a port that helps define a specific region in which the pouch canexpand, and within which the sharp point or edge of the tooth is atleast partially situated to puncture the pouch when it expands. Althoughthe battery cell can expand along multiple expansion paths, the porthelps to define and promote expansion along at least one such path. Theexpansion of the pouch may be also be partially controlled by creating aregion of the pouch of increased expandability relative to the rest ofthe battery cell. In some embodiments the port may expose a region ofincreased expandability. In any of these embodiments, the sharp point ofthe tooth is situated along at least one of the expansion paths of thepouch.

FIG. 23 shows two additional alternative embodiments of pressure releaseteeth. Tooth 450 includes a point 451 and two channels 452. Tooth 455includes two points 456 and two channels 457 extending away from theregion of the point. The structure of tooth 455 (along with otherembodiments that use a sharp edge instead of a point) may help promotethe formation of a ‘tear’ or rip in the pouch to promote gas escape. Ineach of these types of teeth, the channels help to provide a path forthe gases to escape from the battery cell and to ensure the pouch doesnot inadvertently re-seal itself closed (despite the puncture) againstthe tooth. Other orientations and combinations of sharp points andchannels may also be used, as may other combinations of sharp edgesand/or channels.

The tooth is produced from a non-conductive material to help prevent ashort between the interior of the battery cell and the heatsink.

As indicated in FIGS. 5 and 6, a compliant pad 401 contacts every cellvia one of the cell's two large flat surfaces to provide the followingfunctions: (a) Provide uniform pressure distribution for cell life andperformance, (b) provide constant pressure on the cell's active areathroughout the life of the cell, (c) compensate for the cell's thicknesschanges due to the inherent nature during charge and discharge cycles,and (d) compensate for the module's length changes due to the thermalexpansion and contraction of the cell and other module components suchas the heatsinks, pressure plate, and clamping bands.

Pressure Plate Component

FIG. 10 shows a pressure plate 50. Pressure plate 50 is a rigidstructure imparts a static clamp force to the module's main stack ofcells, compliant pads, and heatsinks The structure also provides meansby which the module can be attached inside a battery pack's enclosure.This component may be referred to as a ‘pressure plate’ to accentuatethe primary function. The plate's material is a molded plastic polymerwith defined temperature exposure and flammability ratings. The platehas a prominent flat surface to mate with one end of the module's mainstack, which has two compliant pads at both ends to help distribute andequalize the clamp force.

The side of pressure plate 50 that faces away from the subassemblies hasa matrix of reinforcing ribs 520 to enhance its structural rigidity andcomplement the molded part design practice of targeting a uniform wallthickness. The matrix has a non-uniform pattern because the ribs alsoform pockets which accommodate large electronic components that aresoldered to the module's active control printed-circuit board (PCB)subassembly (not shown). The PCB subassembly includes a circuit boardand components, where the majority of the components are on one side ofthe board. The PCB subassembly is mounted component-side down onpressure plate 50. The nesting of the electronic components preservesvaluable space and contributes to a compact module length at the plate,which helps achieve an excellent power output to physical volume ratio.The plate's pockets are also valuable because they can be used asreceptacles for vibration dampening elements (not shown) to grip theupper surfaces of the large electronic components that are soldered tothe module's active control PCB subassembly. The elements prevent excessstress and fatigue at the solder joints on the PCB. The preferredvibration dampening element is a die-cut pad with an elastomericclosed-cell non-hydroscopic polyurethane foam material andpressure-sensitive adhesive material on one side, which both havedefined temperature exposure and flammability ratings.

The PCB assembly may be either passive or active. Passive PCB assembliesmay be sufficient for smaller battery modules, while larger modules useone or two active PCB assemblies, with one assembly mounted on each ofthe pressure plates at each end of the module. The active PCB controlsubassembly has three right-angle PCB electrical connector headers thatare selectively-soldered to industry-standard plated through holes inthe PCB. All other electronic components are SMT (Surface MountTechnology) devices which are reflow-soldered to industry-standard padson both sides of the PCB. Precautions are taken to ensure a properelectrical isolation between the module's steel bands and the PCBbecause the bands are routed nearby. PCB trace, via, and componentkeep-in and keep-out zones are carefully defined for both sides of thePCB to avoid electrical interference. The module's life capability maybe improved by applying a silicone-based or polyurethane-based conformalcoating to both sides of the PCB, which will reduce the growth ofdendrites between adjacent low-current high-impedance copper traces.

Side 510 of pressure plate 50 is opposite the side with the matrix ofreinforcing ribs 520, and faces the stack of subassemblies. Side 510 maybe flat, or may form a non-flat shallow convex or concave domed profileto further optimize the force distribution within the module's mainstack.

Pressure plate 50 has two shallow tracks 501 to receive thin steelretention bands which impart the static clamp force to the module's mainstack. The tracks have a domed profile to help distribute and equalizethe clamp force. Appropriate dome profiles may be determined bymeasurements taken using existing sensing products specificallydeveloped and marketed for this type of instrumentation application.

Pressure plate 50 also has four passages with recessed sockets 503, 504,505, and 506 (also known as counter-bores) to receive steel fastenercomponents such as cylindrical sleeves, washers, bushings, and retentionbolts to foster a flexible attachment strategy. The presentconfiguration permits a module to be mounted inside a battery pack'senclosure or on a battery station's rack via one of three mountingorientations, which is adequate for the majority of existing andpredicted applications and customer requirements.

The pressure plate may be formed from two separate portions which arevibration-welded together. Each portion would have half of theattachment hole and recessed socket profiles. After welding, completecircular holes and sockets would be formed. The benefit of this approachwould be that the two portions could be molded without long activeslides in the molding tool that are perpendicular to the tool'sprinciple die draw direction.

Pressure plate 50 has two recessed areas 508 to receive a steel busbarnut or nuts (not shown). The nut's design is intentionally simple to bea cost-effective solution. The nut has three threaded holes forattachment. The center hole grips a steel fastener (not shown) thatretains the busbar nut to the pressure plate. The two other holes gripsteel fasteners that attach an external power lug and wiring harness tothe module's negative or positive busbar, which are explained insubsequent sections.

Band Component

FIG. 11 shows steel band 530, which is one of two steel bands used toenvelop the module's main stack of cells, compliant pads, heatsinks, andpressure plates. Each steel band 530 sits in one of the shallow tracks501 of pressure plate 50. Two bands are sufficient and three bands arenot necessary, if the module has seventy-six (76) cells or less. Morebands can be used if desirable. The length of steel band 530 is definedby the required clamp force to properly compress all of the compliantpads in the main stack, and it is retained via an existing released andqualified steel buckle 531 that is permanently crimped onto the band. Ahand-held pneumatic applicator with a pneumatic actuator may be used totension the band and crimp buckle 531, and the applicator may also havea mechanism to trim the band's extra tail after buckle 531 is crimped.Compared to an alternative approach that uses very long steel tie rodsand retention nuts at both ends, using the bands and buckles is a morecompact approach. The use of the same band and buckle and installationprocess for every module fosters a scalable architecture. Anotherapproach is to tension and weld the band, instead of using the crimpedbuckle. The pressure plate 50 may incorporate flat or indented areaswithin the shallow tracks 501 to accommodate the clamping band bucklesand to more evenly distribute the pressure in the region of the buckles.Pressure plate 50 may also have four corner rounds along each track 501to ensure that the tensile forces are equalized in the straight portionsof the two bands.

An existing released and qualified hand-held computer-controlledelectric applicator with a closed-loop servo control may be used insteadof the standard pneumatic actuator. This may increase applied staticclamp force precision and reduce band installation and buckle crimpingprocess cycle times. While the pressure plates and bands help hold thebattery module together physically, the module's busbars (describednext) connect the system electrically.

Busbar Support Component

The electrical interconnection between the module's adjacent cells is animportant feature, which includes the registration of the flexible andfragile cell terminals relative to each other, and includes preventingan accidental contact between adjacent terminals that will not beelectrically connected for the intended application. FIG. 2 shows howall of the cells are securely retained and registered relative to eachother in the module's main stack, except for the cell terminals, e.g.,101 and 102.

FIG. 12 shows a robust, compact, and cost-effective solution using amolded plastic component. The component may be referred to as a ‘busbarsupport’ to accentuate its primary function. The standard busbar support600 a mates with the upper edge of one heatsink 600 a and also envelopsthe two cells 300 a and 310 a. Cells 300 a and 310 are each affixed torespective a side of the heatsink, and each has two electrical terminals(the negative terminals of each battery cell 300 a and 310 a are shownin FIG. 12) which extend through ports in the busbar support. A busbarsupport is used for every subassembly and fosters a scalablearchitecture. For example, busbar support 600 b mates with the edge ofthe second type of heatsink, heatsink 400 b.

FIG. 13A shows another view of a busbar support 600 mounted to heatsink400. The standard busbar support has nine features/functions:

-   -   1. Seven flex tabs 608 (four shown) as well as two wedge-shaped        latches 609 to grip two slots (component 406 in FIG. 5) in a        heatsink.    -   2. Rectangular central port 604 to interface with a thermistor        605 that has an over-molded elastomeric grip.    -   3. Four tapered ports 601 to permit the simultaneous insertion        and registration of four cell terminals.    -   4. Main body 610 that supports a busbar during a cell zipper        fuse actuation incident. By maintaining a separation between any        remainder of the terminal and the busbar, the busbar support        prevents an accidental reconnection of the faulty cell to the        busbar, which could cause a cascading failure mode with the        adjacent cells.    -   5. Two fixed latches 602 and two flex latches 603 to grip two        separate busbar components (not shown) during the laser welding        of the busbars to the cell terminals. This feature helps        eliminate the need for a special laser welding fixture. As        described below, it functions as an assembly jig that secures        the busbar components in registration with the cell terminals        prior and during welding. These latches retain each busbar        component in a substantially fixed position relative to the        heatsink and the attached battery cells. The tapered ports and        main body retain the terminals of each of the battery cells in a        substantially fixed position relative to the heatsink and to the        busbar component.    -   6. Eighteen reliefs 607 to ensure adequate clearance to any        busbar electrical connection rivet.    -   7. Central channel 606 to permit the routing of the module's        voltage sense wiring harness and thermistor wiring harness.    -   8. Four flex fingers (611) to retain the two wiring harnesses        (not shown) before the busbar covers are installed.    -   9. Two screw bosses 612 at the ends for the attachment of the        busbar covers.

In addition, FIGS. 13B and 16 show a second busbar support 650 that hasbeen developed to envelop only one cell if a module has an odd cellcount. While this decision causes another component to be released andproduced, it fully respects the principle that every cell terminal beregistered and protected from an accidental contact with an adjacentterminal. The module's vibration endurance robustness may be improved byadding two or more additional slots in the heatsink near the centerand/or adding two more wedge-shaped latches in the busbar support.

Busbar Components

Busbar components consist of busbar jumpers, which electrically connectthe module's adjacent cells, and busbar terminals, which electricallyconnect one or more battery cell terminals to each of the externalterminals of the battery module. FIG. 14 shows a robust, compact, andcost-effective interconnection approach using these busbar components toenhance the module's life capability. This approach avoids usingthreaded fasteners for any of the electrical connections inside themodule and to instead use precision welds that are produced withadaptive automatic computer-controlled processes.

FIG. 14 shows several busbar jumpers 700 each held by busbar supports600. For each of the busbar supports through which a battery cell'sterminal extends, the busbar jumper connected to that terminal isgripped between the support's fixed latch and its opposing flexiblelatch. The latches retain the busbar jumper against the terminal andprevent its movement.

FIG. 15 shows a bimetallic busbar jumper 700. The battery module uses agroup of busbar jumpers 700, each including a copper portion 701 that islaser welded to a group of cell negative terminals which are made of acopper material, and an aluminum portion 702 that is laser welded to agroup of cell positive terminals made of an aluminum material. Thebusbar jumper's 180-degree bends 703 define an inside surface 704 inwhich the cell terminals are nested during assembly. The portions of thebusbar that have the bends are continuous pieces of metal. Precisionlaser welding is used to partially melt and metallurgically connect thebusbar jumpers to the terminals in order to avoid ultrasonic weldingthat could inflict too much energy into a cell terminal and in turndamage a cell's internal electrical connections. A liquid weldingtreatment is applied to the outer surface (opposite inner surface 704)of the busbar jumper's bends 703. During welding, laser energy will beaimed at this surface. This treatment creates a finish that decreasesthe reflectivity of the laser beam during laser welding of the highlyreflective surfaces of both aluminum and copper. This treatment may be aNickel or Tin coating that provides for better absorption of the Nd-YAGlaser beam wavelength. This allows one to minimize the energy requiredto weld and allows for the welding of cell terminals to be conductedwithout exceeding a maximum temperature limit of the cell terminal'sseal. The laser beam's energy penetrates the busbar's 180-degree bend703 and creates a molten bead inside the busbar's bend 704 and at thetip of the cell's terminal (not shown). The welding laser is aimed atthe busbar's bend 703 at an angle substantially head-on to the end ofthe battery terminal and toward the outer surface of the bend as shownby angle of attack 708.

FIG. 25 shows an additional view 735 of the configuration of a weldinglaser 730 and a bimetallic busbar jumper 700, with the laser beam 733directed at the busbar's bend at an angle of attack 708 that issubstantially head-on to the end of the battery terminal. A second view740 shows the configuration of view 735 as seen along line of reference736 (i.e., view 735 rotated 90 degrees around the vertical z axis). View740 shows laser 730 moving from the right side end of the busbar's bend742 to the left, where the laser beam 733 moves in a direction of travelparallel to the channel, with the laser beam 733 directed at a slightangle 741 with respect the bend 742, with angle 741 opposing thedirection of travel of the laser 730 to prevent the laser beam frombackreflecting into the laser optics and causing damage. This results inlaser beam 733 directed at an angle slightly less than perpendicular tothe direction of travel of the laser beam. During welding, the laser 730may move relative to the busbar and battery terminal being welded, thebusbar and battery terminal assembly may move relative to the laser, orboth may be moved relative to each other. The result in any case is thatthe busbar and battery terminal are attached to each other along thelength of the channel in which the battery terminal resides.

FIG. 26 shows side views of the attachment of a busbar component tobattery cell terminal both before and after attachment. View 770 shows abend 704 in a busbar 700 forming a channel in which battery terminal 771is positioned. View 775 shows these components after welding in whichthe battery terminal 776 is attached to an inside corner of a bend in abusbar 777 by a resolidified pool of metal 778.

Welding processes such as laser welding or other conventional weldingprocesses may not be practical to use to join a bimetallic jumperbusbar's two portions together due to the dissimilar materials and knownmetallurgical constraints. Instead, busbar jumper 700 employs anultrasonic roller seam welding process to create a linear weld 705. Theultrasonic welding of the jumper busbar's two portions is performedseparately from the module so that ultrasonic energy is not introducedinto a cell terminal, in turn risking damage to a cell's internalelectrical connections. As noted above, the busbar supports act aswelding jigs. The busbar supports hold the busbar components in placewith the cell terminals nested in the slots defined by the bends in thebusbars until the busbars are laser welded to the terminals as discussedabove.

To further balance and optimize the electrical current characteristicsof the bimetallic jumpers, the cross-sections, widths and/or thicknessesof the jumper busbar's two portions—whose materials are aluminum andcopper—may be independently tailored to achieve similar resistancesthrough each portion. In manufacturing the busbar jumpers, extrudedcut-to-length profiles for one or both of the bimetallic jumper busbar'stwo portions may be used instead of sheet stamping and forming processesin order to reduce cost. In one configuration, the copper portion of thebusbar jumper is stamped and the aluminum portion is extruded.

FIG. 16 shows a busbar terminal 750 secured in part by busbar supports600 and 650. Busbar supports retain the busbar terminals in the samemanner as the supports retain the busbar jumpers. Busbar terminal 750 islaser welded to a corresponding terminal of battery cells 300 a, 310 a,and 320. Battery modules use a monometallic negative busbar terminalwith a copper material at one end of the module's main stack and amonometallic positive busbar terminal with an aluminum material at theother end of the module's main stack. The busbar terminals are securedby steel busbar nuts 760 that are attached to the sockets 508 of thepressure plate 50. The busbar terminal 750 has a tapered central portion751 that acts as a module fuse if a worst-case electrical overloadincident occurs. The fuse will have a tendency to melt at the narrowportion where the current density if the highest. The module's safetycapability may be improved by adjusting the actuation response time ofthe two module fuses by adding zipper fuse holes and slots to the busbarterminals in a similar manner to the way zipper fuses are integratedinto the battery cell terminals.

FIG. 17 shows the installation of busbar terminal 750 to pressure plate50. Busbar terminal 750 is attached to a steel busbar nut (not visibleunder busbar terminal in FIG. 17). The busbar nut is attached to one ofthe pressure plate's sockets 508 a. Busbar terminal 750 is connected toan external power lug and wiring harness (not shown) as describedearlier. In addition, a stamped copper busbar nut bridge 780 may beconnected to busbar terminal 750 and also connected to pressure platesocket 508 b through busbar nut 760 b. Busbar nut 760 b is secured topressure plate 50 through a center hole that grips a steel fastenerdisposed in pressure plate socket 508 b. The bridge is an accessory thatpermits an optional attachment site for the module-to-module high-powerwiring harness.

Wiring Attachments

FIG. 18 shows a busbar terminal 750 with two variations of clips used toattach wiring, such as voltage sense wiring harnesses, to busbarterminals and busbar jumpers. From one side, clip 791 is u-shaped andsubstantially convex, while clip 790 is w-shaped. Either or both ofclips 790 and 791 may be used to connect wiring. Voltage sense wires areultrasonically welded to the clips prior to attaching the clips to thebusbar components. The clips have one or more teeth 793 that bite intothe busbar jumpers or terminals so that the clips can be positioned andretained in place until a laser welding operation fastens the clips tothe busbar. The clips may be of stamped copper or aluminum correspondingto and compatible with the type of busbar to which they will beattached. Clips have notching 792 for one metal type to indicate thetype of clip for manufacturing using automatic vision systems. Theseclips are laser welded to the busbar components at the same time thebusbar components are welded to the battery cell terminals and share acommon weld. Using the same welding technique described above forattaching busbar components to battery terminals, a laser is directedthrough the clip and the underlying busbar component and pointed at theend of the terminal that rests in the u-shaped bend of the busbarcomponent. In so doing, a single welding operation welds all threecomponents (the clip, the busbar component, and the battery terminal) atthe same time. The u-shaped clips may also be laser welded to the busbarcomponent without sharing a common weld.

FIG. 19 shows a side-view of w-shaped clip 790 with the clip's teeth 793bent slightly inward for installation on a busbar. Teeth may or may notbe required to secure the clip to the busbar until it is welded if theclip is designed with an interference fit such that the interferencewould provide the retaining function.

FIG. 20 shows a busbar terminal 750 with a clip 794 for attaching athermistor 795 to the busbar terminal. The thermistor's head is bondedinside the clip's retainer with a dispensed cure-after-assembly epoxyadhesive. The neck of the thermistor's head contacts the adjacent tab796 so that the head has a defined repeatable location. Coined chamfers797 to the retainer's upper edges help prevent damage to thethermistor's head when it is installed.

Busbar Covers

FIG. 1 shows three busbar covers 40. Battery modules use a group ofmolded plastic covers to protect the module's busbars and other internalcomponents, such as the voltage sense wiring harness and thermistorwiring harness, from any accidental contact by external foreign objects,especially if they are metallic.

FIG. 21 shows a busbar cover 40 a without the cover's main flat skin sothat the relative fits may be witnessed. Busbar cover 40 b is alsoshown, including the cover's main flat skin. Each of the covers has amatrix of reinforcing ribs, including 801, 802 and 803, to enhance itsstructural rigidity and to also redirect and distribute any adverseexternal forces to the module's busbar supports and heatsinks instead ofthe busbar terminals 750, busbar jumpers 700 and/or cell terminals.Busbar covers envelop the module's busbars to help prevent adjacentbusbars from contacting each other and causing electrical short circuitpaths during a worst-case electrical overload incident or severe vehiclecrash. Certain ribs, e.g., rib 802, extend deeper into the batterymodule than other ribs and in between the busbar jumpers, e.g., 803, tohelp prevent contact between adjacent busbars, while ribs such as 803are less deep to avoid distributing forces to the busbar terminals,busbar jumpers or cell terminals. Alternatively, the battery module mayuse lower-cost, simpler covers which have an overlap joint and fewervertical contact tabs. The disadvantage with this latter approach isthat the module's robustness to withstand vertical external forces maybe diminished.

Scalable Architecture

The above described features yield a scalable architecture. The term‘scalable architecture’ refers to a flexible configuration whichfacilitates the rapid engineering, development, qualification, andproduction of battery modules that have different quantities of batterycells, subgroups with cells that are electrically connected in parallel,and subgroups that are electrically connected in series. Thisflexibility enables a battery supplier to tailor the electricalcharacteristics of many different modules and to satisfy diversecustomer performance specifications. For example, the presentA123Systems prismatic battery module family with the ‘3P’ configurationis shown in FIG. 22. The seven members of this family are the 23S3P,22S3P, 16S3P, 13S3P, 11S3P, 6S3P, and 1S3P modules, identifiedrespectively in FIG. 22 as 907, 906, 905, 904, 903, 902, and 901.

FIG. 24 shows various busbar component configurations for the followingmembers of the A123Systems prismatic battery module family, 13S3P,23S2P, 4S2P, and 4S6P identified respectively in FIG. 23 as 950, 951,952, and 953.

1. A battery comprising: a battery cell having two voltage terminals anda flexible sidewall; a wall structure against which the battery cell islocated, said wall structure including a sidewall that is adjacent tothe sidewall of the battery cell; and a tooth structure that extendsaway from the sidewall of the wall structure and towards the sidewall ofthe battery cell, wherein the tooth structure includes a distal endsufficiently sharp to puncture the flexible sidewall of the battery cellwhen the flexible sidewall of the battery cell is forced up against thetooth structure due to a build up of excess pressure inside the batterycell.
 2. The system of claim 1, wherein the battery cell is a prismaticbattery cell.
 3. The system of claim 2, wherein the distal end is apoint.
 4. The system of claim 2, wherein the distal end is an edge. 5.The system of claim 3, wherein the tooth further comprises a channelextending away from the region of the sharp feature to allow gaseswithin the region of the point to move away from the battery cell. 6.The system of claim 3, wherein the tooth further comprises a secondsharp point and a channel between the first and second sharp points toallow gases between the points to move away from the battery cell. 7.The system of claim 2, wherein the first battery cell comprises a regionof increased expandability relative to the rest of the battery cell, theregion defining a specific expansion path for the battery cell, andwherein the distal end is situated along the specific expansion path. 8.The system of claim 7, wherein the region of increased expandabilitycomprises a port exposing a puncturable portion of the battery cell. 9.The system of claim 8, wherein the tooth extends at least partially intothe port.
 10. The system of claim 1, wherein the sidewall of the wallstructure is a part of a heatsink.
 11. The system of claim 1, whereinthe sidewall of the wall structure is a busbar support that is mountedto a heatsink.